This invention is directed to a method for making laminated plastic cards which incorporate electronic elements such as integrated circuit microchips.
Laminated electronic cards are widely used in the radio-frequency identification (RFID) field for applications which include remotely readable electronic key cards and identification cards. Each electronic card may contain a radio-frequency transponder system which typically includes a transponder microchip with associated elements such as tuning capacitors and a radio-frequency antenna. The electronic components of the card are contained between two or more sheets of plastic laminated to each other by application of heat and pressure to top and bottom exterior surfaces of the card assembly.
In existing card lamination processes the electronic components are supplied to the card manufacturer on a continuous roll of polyester which may be 2 inches wide by 1000 feet in length, with the electronic circuits spaced along the roll at, e.g. two inch intervals. Each electronic circuit may include a radio-frequency antenna circuit printed on the polyester sheet, an integrated circuit such as a flip chip integrated circuit electrically connected to the antenna, and any other components such as a tuning capacitor that may be required for the operation of the particular circuit. The electronic circuit as supplied on the roll is complete and ready for insertion into a card.
This is accomplished by punching out from the roll portions of polyester sheet carrying each electronic circuit to obtain an inlay or insert which are picked up and placed one-by-one by a robotic device onto a blank first sheet of plastic. The individual inlays are held in place on this blank sheet by means of a pre-applied adhesive or by laser welding. The electronic circuit inlays are then covered with a second sheet of plastic placed over the first sheet of plastic. These two sheets of plastic range between 2 and 10 mils in thickness and together make up the core of the laminated cards. Additional sheets may be placed over the first and second sheets, for example, graphics layers and protective clear overlays. The multiple sheets are then laminated to each other by application of sufficient heat and pressure to cause partial fusion of the contacting surfaces of the adjacent sheets. The first and second plastic sheets are typically of vinyl which is not compatible with the polyester carrier sheet of the electronic circuit inlay. That is, the vinyl does not make a dependable lamination bond with the polyester. For this reason, the polyester sheet is limited to an interior portion of the card, leaving a sufficient border around the inlay, e.g. a xe2x85x9th  or xc2xc inch width, of the first and second sheets of vinyl to bond to each other around the electronics inlay.
The process just described is cumbersome because of the number of operations involved, including separation of the electronics inlays from the supply roll, transferring each inlay to the plastic sheet and fastening the inlay to the plastic sheet.
In applicant""s prior application Ser. No. 09/299,944 a method for the continuous extrusion of electronic cards with inlaid electronic circuits or devices was disclosed. While continuous extrusion addresses some of the shortcomings of the prior art, it requires specialized extrusion equipment.
A simpler and faster method of making electronic cards is still needed which makes use of machinery and processes familiar to the industry such as lamination processes and equipment.
This invention addresses the aforementioned shortcomings, and provides a method for large volume production of laminated cards containing electronic elements. The novel method includes the steps of providing a number of electronic circuits supported on a carrier sheet; perforating the carrier sheet to define a carrier web having a number of carrier cards wherein each carrier card supports at least one of the electronic circuits. Each carrier card has a number of carrier card edges and each carrier card is connected to one or more adjacent carrier cards by one or more links each having a link width small in relation to the total length of the carrier card edges. The carrier web with the electronic circuits is interposed between a top sheet and a bottom sheet of plastic material; applying heat and pressure to the top sheet and the bottom sheet sufficient to bond the top and bottom sheets to each other into a laminate sheet containing the carrier web and the electronic circuits. The laminate sheet is cut so as to define a number of laminate cards, each laminate card having a number of laminate card edges and containing between the laminate card edges at least one carrier card; the laminate card edges being of greater length than the carrier card edges such that the top and bottom sheets of the carrier card overlap the carrier card edges to form border areas. The top and bottom sheets are free to contact and fuse or otherwise bond to each other over these border areas, so as to hide the edges of the carrier card, except where the links of the carrier card are severed along the edge of the carrier card. As a result, the edges of the carrier card are recessed from the edges of the laminate card such that exposure of the carrier card along the laminate card edges is substantially limited to the width of the links thereby to provide for adhesion between the top sheet and the bottom sheet along the laminate card edges.
The carrier sheet may be made by cutting a length of a continuous carrier roll, the carrier roll being pre-loaded with the electronic circuits such that the circuits are arranged in an n by m matrix on each carrier sheet. The electronic circuits may each include or consist of, for example, a radio frequency antenna connected to a radio frequency transponder integrated circuit.
The carrier sheet may be of polyester and the top sheet and the bottom sheet may be of vinyl. The exposed link edges may be located at one or more corners of the finished laminate card. For example, each carrier card may have four links located at the four corners of a rectangular card which result in exposed link edges at four card corners of the laminate card.
The method according to this invention may further include the step of placing a graphics sheet over one or both of the top sheet and the bottom sheet prior to the step of applying heat and pressure, such that the resulting laminate sheet also includes the graphic sheet to provide graphics visible on one or both of sides of the finished laminate card. It may also be desirable to apply a clear overlay sheet over the graphics sheet prior to the step of applying heat and pressure such that the overlay sheet is also included in the laminate sheet and the graphics layers on each finished laminate card are protected against wear during subsequent use of the laminate card.
In addition to the novel method just summarized, this invention also includes a laminated electronic card having first and second sheets of similar thermoplastic material such as vinyl, an intermediate carrier sheet of a different thermoplastic material substantially incompatible with lamination to vinyl, such as polyester, and an electronic circuit on the carrier sheet between the first and second plastic sheets, the first and second sheets being bonded to each other along a card edge, preferably including a laminated border area of significant width such as xe2x85x9th  or xc2xc inch in width, such that the carrier sheet is exposed only along relatively small segments of the laminated card edge thereby to minimize likelihood of delamination of the first and second sheets along the laminated card edge. In one form of the laminated electronic card of this invention the carrier sheet is exposed only along corner portions of the card edges, and the small segments are each no more than about one quarter inch in length along the card edge. The electronic circuit contained between the first and second sheets may include or consist of a radio frequency antenna, for example an antenna circuit printed on the carrier sheet, connected to a radio frequency transponder integrated circuit. The laminated electronic card may also include a graphic sheet laminated to exterior surfaces of one or both of the first and second sheets, and a clear overlay sheet applied over the graphic sheet to protect the graphics sheet against wear during use of the card.
The finished laminated card obtained by the process of this invention resembles the electronic cards obtained by the previously disclosed continuous extrusion process of the related application Ser. No. 09/299,944 in that the edges of the finished card are of uniform material along the card edges except for short exposed sections of a layer of different material used as a carrier layer for the inlaid electronic circuit, and to this extent, the prior disclosure is incorporated herein.
These and other improvements, features and advantages of the method and the card of this invention will be better understood from the following detailed description and accompanying drawings.